Temporal studies of a MWPC at high pressures

We report on results achieved by recording the waveforms produced by a common multiwire proportional chamber (MWPC). Data were taken using a 90Sr source at pressures between 6 and 43 atm and voltages over a range of gains allowing the current signal to be viewed directly into 50 Ω on a Tektronix CSA 803 digital processing oscilloscope. A systematic study was made using an argon-methane (90-10) gas mixture. A fastest rise time per amplitude of 40 ps/mV was observed at 22 atm. Faster signals have been observed by mixing a small fraction of freon 13B1 in an argon-methane (90-10) gas mixture, thus limiting the charge transport efficiency to a region near the anode wires. This yielded a rise time per amplitude of ≅ 5 ps/mV. In this way, average rise times in the raw signals of a few hundred picoseconds have been observed at 20 atm. Time spectra acquired with the use of an external scintillator trigger are also shown. (orig.)